Economic fermentation broth

Some of the economic hurdles and process cost centers of this conventional carbohydrate fermentation process, schematically shown in Eigure 1, are in the complex separation steps which are needed to recover and purify the product from the cmde fermentation broths. Eurthermore, approximately a ton of gypsum, CaSO, by-product is produced and needs to be disposed of for every ton of lactic acid produced by the conventional fermentation and recovery process (30). These factors have made large-scale production by this conventional route economically and ecologically unattractive. 

The batch and fed-batch procedures are used for most commercial antibiotic fermentations. A typical batch fermentor may hold over 150,000 Hters. When a maximum yield of antibiotic is obtained, the fermentation broth is processed by purification procedures tailored for the specific antibiotic being produced. Nonpolar antibiotics are usually purified by solvent extraction procedures water-soluble compounds are commonly purified by ion-exchange methods. Chromatography procedures can readily provide high quaHty material, but for economic reasons chromatography steps are avoided if possible. 

Some products are precipitated from the fermentation broth. The insoluble calcium salts of some organic acids precipitate and are col-lec ted, and adding sulfuric acid regenerates the acid while forming gypsum (calcium sulfate) that constitutes a disposal problem. An early process for recovering the antibiotic cycloserine added silver nitrate to the fermentation broth to precipitate an insoluble silver salt. This process was soon obsolete because of poor economics and because the silver salt, when diy, exploded easily. 

General criteria for the economically feasible recovery of amino adds from the fermentation broth are ... 

Initially fermentation broth has to be characterised on the viscosity of the fluid. If the presence of the biomass or cells causes trouble, they have to be removed. Tire product is stored inside the cells, the cells must be ruptured and the product must be freed. Intracellular protein can easily be precipitated, settled or filtered. In fact the product in diluted broth may not be economical enough for efficient recovery. Enrichment of the product from the bioreactor effluents for increasing product concentration may reduce the cost of product recovery. There are several economical methods for pure product recovery, such as crystallisation of the product from the concentrated broth or liquid phase. Even small amounts of cellular proteins can be lyophilised or dried from crude solution of biological products such as hormone or enzymes.2,3... 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

Medium scale process are usually associated with commodity organic chemicals and with the substitution of natural products in place of materials from other sources. These processes generally produce stable products and utilise conventional process operations for the recovery of the product. The economic viability of such processes is sensitive to the concentration of the product in the fermenter broth. 

Reverse micelles are self-organized aggregates of amphiphilic molecules that provide a hydrophilic nano-scale droplet in apolar solvents. This polar core accommodates some hydrophilic biomolecules stabilized by a surfactant shell layer. Furthermore, reverse micellar solutions can extract proteins from aqueous bulk solutions through a water-oil interface. Such a liquid-liquid extraction technique is easy to scale up without a loss in resolution capability, complex equipment design, economic limitations and the impossibility of a continuous mode of operation. Therefore, reverse micellar protein extraction has great potential in facilitating large-scale protein recovery processes from fermentation broths for effective protein production. 

Several methods have been explored for the economical recovery of lactic acid from fermentation broth including extraction with solvent, electrodialysis, ion-exchange adsorption (see [14] for review), and reverse osmosis [15]. Wang et al. 

In research aimed at lower chemical costs for enhanced oil recovery, we are attempting a separation of this type, biopolymer from fermentation broth. The motivation is to eliminate the conventional precipitation of polymer by alcohol addition, a step which contributes a substantial fraction of production cost, perhaps as much as 40%, with the necessity to recover alcohol for recycle (Figure 1). Precipitation is necessary to prepare a dry product, economical to ship. (Concentrated broth, prepared at a central facility, is also proposed, at a penalty in transportation costs.)... 

Unfortunately the enzyme titer in the fermentation broth, even after classical mutation and several years of process development, was too low for the biocatalyt-ic process. With respect to the economics, the gene encoding for glutaryl-7-ACA acylase has been cloned, sequenced and expressed in E. coli to produce sufficient amounts. The enzyme titer could be increased by a factor of more than 100. Even the purification of the enzyme became much easier and resulted in higher yields with less side-activities, e.g., esterases. Two chromatographic purification steps were substituted by crystallization of the enzyme. The enzyme crystals could be stored long term without deactivation. To allow for reuse, the glutaryl-7-ACA acylase was immobilized on a polymeric carrier. 

In many cases, a fermentation process must be a high solids process in order to be economic. Substrate, microbes, or product, or all three together may be considered as solids. In general, fermentation broths of mold and streptomyces exhibit non-Newtonian behavior, either Bingham... 

Although considerable effort in research and development has been devoted to the removal of VOCs from aqueous streams this technique has not yet been introduced into the industry. Potential mixtures like waste-water streams that could be treated are more complex, the economical value of the recovered substances is low. Even when a pure substance like phenol can be efficiently removed and recovered from water competing processes like biological treatment or adsorption are cheaper and better introduced. Applications may be found in the future in biotechnological processes where high-value products can be separated from a fermentation broth and can be concentrated and purified in the same step. 

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